| Abbreviation | Definition |
|---|---|
| INFT | Informant |
| INLET | INtelligence LETter for the President |
| INT | Intelligence Not Tested |
| INTC | INTelligence Corps |
| INV | INVestigative |
| IO | Identification Orders |
| IOB | Intelligence Oversight Board |
| IOC | Interception Of Communication |
| IOCI | International Organized Crime Index |
| IP | Indianapolis Field Office |
| IPAL | Information and Privacy Acts Litigation |
| IPTF | International Police Task Force |
| IPTU | International Prisoner Transfer Unit |
| IPU | Initial Processing Unit |
| IRU | Investigation Review Unit |
| IS | Internal Security |
| ISA | Internal Security Act |
| ISD | Internal Security Division |
| ISINT | ISraeli INTelligence Service |
| ISS | Indices Search Slip |